Abstract Understanding the impact of recreational cannabis legalization on treatment of substance use disorders (SUD) is the goal of this research. Drawing upon treatment centers recruited in our prior studies, we propose to collect two waves of organization-level data from 350 SUD treatment organizations comprising 3 mutually exclusive groups: (1) centers located in states where recreational cannabis is legal (?legalization states?); (2) centers in states that prohibit recreational cannabis but allow medical cannabis (?medical cannabis states?); and (3) centers in states that prohibit medical and recreational cannabis (?prohibition states?). These three groups are foundational to achieving the project?s Specific Aims, which are (1) to compare cannabis treatment admissions in treatment centers located in legalization states, medical cannabis states, and prohibition states as well as to examine changes in treatment admissions over time; and (2) to examine whether treatment delivery for cannabis use disorder (CUD) is altered in response to legal recreational cannabis availability. Controlling for the organizational, legal, and socioeconomic environment, we will examine admissions for cannabis for adults 21 and older and for individuals under age 21. We will examine heterogeneity in state cannabis laws, including important nuances in policies toward dispensaries, home cultivation, and total production, to assess treatment system impacts of each policy provision as well as to compare impacts of centers in early legalization states (CO and WA) relative to centers in later legalization states. Based on substitution and complementary hypotheses, we will also examine patterns of change in admissions for other SUD diagnoses, such as nonmedical prescription opioids, and in sources of referrals, differentiating between clients with CUD from those presenting due to a court mandate or in lieu of incarceration. Measures will examine changes in inter- organizational relationships between centers and community institutions, such as educational institutions, primary care, and the criminal justice system. Because treatment admissions may be affected by how states are implementing health reform, we will control for state-level approaches to health reform as well as other state-level characteristics. This study will also examine if and how screening tools and treatment practices are adapted or reinvented to fit the needs of patients with cannabis-related problems. Using resource dependence theory, absorptive capacity, and diffusion of innovation theory, we will compare the effects of organizational and external socioeconomic and legal factors on the adoption of treatment practices for CUD, including off- label use of medications. In addition, we will focus on management?s proactive strategizing (or absence thereof) in response to legalization, such as adaptations in marketing campaigns. These innovative findings will assist the SUD treatment field to build a body of evidence-based management strategies related to CUD treatment, and will set the stage for understanding how these strategies are linked to organizational outcomes. Addressing such questions is critical as other states consider cannabis legislation initiatives.